1. Field of the Invention
The present invention relates generally to auger systems for constructing auger cast piling and, more particularly, to an apparatus for monitoring grout pressure in an auger assembly during construction of an auger pressure grouted pile.
2. Discussion of the Prior Art
It is known to form structural piles through the use of pressure grouting techniques, wherein a bore is formed in the earth at the site of a pile, and is filled with grout under pressure to complete the piling.
A conventional auger assembly for use in such operations includes an upright support frame that can be positioned adjacent a pile site and supported by means of a mobile crane or the like. An auger assembly is associated with the support frame, and includes an elongated, flighted auger having a hollow central shaft, and a support means for supporting the auger on the frame for relative rotational and vertical movement. A grout supply means is also provided in the form of a truck-mounted grout pump or the like for supplying grout through a flexible hose to the upper end of the auger during lifting thereof, the grout flowing through the auger and from the lower end into the bore.
During a pile-forming operation, the auger is rotated while down pressure is applied so that the auger is driven into the earth. When the auger has reached a desired depth, it is withdrawn, again being rotated to remove soil from the bore so formed. Simultaneously, fluid grout is directed under pressure through the auger shaft to cast the pile.
In order to ensure that the grout is supplied to the bore in an amount sufficient to fill the cross-sectional area of the bore as the auger is raised, it is necessary to monitor and control the supply of grout at all times during casting of the pile. Such control is normally achieved by calculating the necessary amount of grout to fill the bore, and supplying more than the calculated amount. In this manner, a head of grout is maintained in and around the auger at all times so that the entire cross-sectional area of the bore is filled throughout the height of the pile and any voids communicating with the bore are also filled.
The strength of a completed pile is dependent on proper placement or installation of the grout in the pile. One method of verifying proper casting includes the use of a pressure monitor in the grout line at the grout pump. In theory, by maintaining a minimum predetermined pressure at the pump, a sufficient pressure will exist at the lower end of the auger to ensure proper installation. However, in practice it is sometimes necessary to pump grout to a height of 80 feet or more above the ground to the upper end of the auger such that the pressure at the pump far exceeds the pressure at the lower end of the auger, and there is no guarantee that the pressure in the bore is greater than the predetermined minimum pressure desired.